Evaluation of Elevated IGF-1 Levels

Introduction to IGF-1 Interpretation

The American College of Cardiology and other endocrinology guidelines suggest that an IGF-1 level of 183 ng/mL in a 71-year-old female is most likely normal for age, as IGF-1 physiologically declines with aging, and this value typically falls within the reference range for this demographic 1, 2, 3, 4.
IGF-1 must be interpreted against age-matched, sex-matched reference ranges because levels decline substantially with aging 5, 6, 7.

If IGF-1 is confirmed elevated for age, acromegaly is the most important diagnosis to exclude due to its significant impact on cardiovascular mortality and morbidity 1, 2, 3, 4.
Clinical features to assess for acromegaly include acral enlargement, coarsened facial features, frontal bossing, prognathism, headaches or visual field defects, diabetes mellitus or glucose intolerance, and hypertension 1, 2, 3, 4.
The diagnostic workup for suspected acromegaly includes measuring serum growth hormone level, and if GH ≥1 ng/mL, proceeding with an oral glucose tolerance test 1, 2, 3, 4.
An oral glucose suppression test is used to confirm GH excess, where failure to suppress GH below 1 ng/mL after glucose load confirms the diagnosis 5, 6, 7.
Pituitary MRI is recommended to identify adenoma in cases of confirmed GH excess 1, 2.

Poorly controlled diabetes mellitus can cause falsely elevated IGF-1 levels without actual GH excess 5, 6, 7.
Hepatic or renal failure may produce spuriously elevated IGF-1 measurements 5, 6, 7.
Inter-assay variability is substantial for IGF-1 measurements, requiring the use of laboratory-specific reference ranges 5, 6, 7.

Severe hypothyroidism suppresses IGF-1 generation 5, 6, 7.
Malnutrition or low energy states decrease IGF-1 while potentially increasing GH (GH resistance) 8.
Oral estrogen use reduces hepatic IGF-1 generation 5, 6, 7.

Verify the IGF-1 is truly elevated by comparing to the specific upper limit of normal for age and sex in the laboratory's reference range 5, 6, 7.
If elevated, measure random serum GH level 1, 2, 3, 4.
If GH ≥1 ng/mL, perform an oral glucose tolerance test with GH measurements 1, 2, 5, 6.
If GH fails to suppress <1 ng/mL, order pituitary MRI and refer to endocrinology 1, 2.